Her hair is brown and tied back into a professional-looking ponytail. She wears a blue shirt, tan sweater and delicate gold chain. It’s the first time she has met the man sitting across from her, and she looks out at him, her eyes curious.

…

Now, obviously this work raises all kinds of issues, and even on a practical level, real obstacles remain. Jeff Cohn, a psychologist at the University of Pittsburgh, studies the relationship between physical movements and emotion and says signals from the face, voice and body are incredibly complicated to interpret.

“Individuals vary a lot in how expressive they are,” Cohn explains. “You know, if I’m someone who is very expressive and I smile frequently, [even] when I’m depressed and smiling less, I may still smile more than you do if you’re a tight-lipped, not very emotive individual.”

This means, Cohn says, that using Ellie in the way blood tests are used — as proof positive of one diagnosis or another — will be really difficult.